Elastic averaging coupling

ABSTRACT

A passive optical alignment coupling between an optical connector having a first two-dimensional planar array of alignment features and a foundation having a second two-dimensional planar array of alignment features. One of the arrays is a network of orthogonally intersecting longitudinal grooves defining an array of discrete protrusions that are each in a generally pyramidal shape with a truncated top separated from one another by the orthogonally intersecting longitudinal grooves, and the other array is a network of longitudinal cylindrical protrusions. The cylindrical protrusions are received in the grooves, with protrusion surfaces of the cylindrical protrusions in contact with groove surfaces and the top of the discrete protrusions contacting the surface bound by the cylindrical protrusions. The optical connector is removably attachable to the foundation to define a demountable coupling, with the first array of alignment features against the second array of alignment features to define an elastic averaging coupling.

PRIORITY CLAIM

This application: (a) is a continuation of U.S. patent application Ser.No. 17/167,068 filed on Feb. 3, 2021; and (b) claims the priority ofU.S. Provisional Patent Application No. 62/969,536 filed on Feb. 3,2020. These applications are fully incorporated by reference as if fullyset forth herein. All publications noted below are fully incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to coupling of light into and out ofoptoelectronic components (e.g., photonic integrated circuits (PICs)),and more particular to the optical connection of optical fibers to PICs.

Description of Related Art

Photonic integrated circuits (PICs) or integrated optical circuits arepart of an emerging technology that uses light as a basis of operationas opposed to an electric current. A PIC device integrates multiple (atleast two) photonic functions and as such is analogous to an electronicintegrated circuit. The major difference between the two is that aphotonic integrated circuit provides functionality for informationsignals imposed on optical wavelengths typically in the visible spectrumor near infrared 850 nm-1650 nm.

PICs are used for various applications in telecommunications,instrumentation, and signal-processing fields. A PIC device (in the formof a photonic chip package) typically uses optical waveguides toimplement and/or interconnect various on-chip elements, such aswaveguides, optical switches, couplers, routers, splitters,multiplexers/demultiplexers, modulators, amplifiers, wavelengthconverters, optical-to-electrical (O/E) and electrical-to-optical (E/O)signal converters (e.g., photodiodes, lasers), etc. A waveguide in a PICdevice is usually an on-chip solid light conductor that guides light dueto an index-of-refraction contrast between the waveguide's core andcladding.

One of the most expensive components within photonic networks are thefiber-optic connectors. For proper operation, a PIC typically needs toefficiently couple light between an external optical fiber and one ormore of on-chip waveguides. It is often necessary for PIC devices tohave optical connections to other PIC devices, often in the form anorganized network of optical signal communication. The connectiondistances may range from a several millimeters in the case ofchip-to-chip communications up to many kilometers in case of long-reachapplications. Optical fibers can provide an effective connection methodsince the light can flow within the optical fibers at very high datarates (>25 Gbps) over long distances due to low-loss optical fibers. Forproper operation, a PIC device needs to efficiently couple light betweenan external optical fiber and one or more on-chip waveguides. Anadvantage of using light as a basis of circuit operation in a PIC deviceis that its energy cost for high-speed signal transmission issubstantially less than that of electronic chips. Thus, efficientcoupling between PIC devices and other optical devices, such as opticalfibers, that maintains this advantage is an important aspect of PICs.

One approach to coupling optical fibers to a PIC device (or a PIC chippackage) is to attach an optical fiber array to the edge of the PICchip. Heretofore, optical fiber arrays are aligned to elements on thePICs using an active alignment approach in which the position andorientation of the optical fiber(s) is adjusted by machinery until theamount of light transferred between the fiber and PIC is maximized. Thisis a time-consuming process that is generally done after the PIC isdiced from the wafer and mounted within a package. This postpones thefiber-optic connection to the end of the production process. Once theconnection is made, it is permanent, and would not be demountable,separable or detachable without likely destroy the integrity ofconnection for any hope of remounting the optical fiber array to thePIC. In other words, the optical fiber array is not removably attachableto the PIC, and the fiber array connection, and separation would bedestructive and not reversible (i.e., not reconnectable).

The current state-of-the-art attempts are to achieve stringent alignmenttolerances using polymer connector components, but polymers have severalfundamental disadvantages. First, they are elastically compliant so thatthey deform easily under external applied loads. Second, they are notdimensionally stable and can change size and shape especially whensubjected to elevated temperatures such as those found in computing andnetworking hardware. Third, the coefficient of thermal expansion (CTE)of polymers is much larger than the CTE of materials that are commonlyused in PIC devices. Therefore, temperature cycles cause misalignmentbetween the optical fibers and the optical elements on the PIC devices.In some cases, the polymers cannot withstand the processing temperaturesused while soldering PIC devices onto printed circuit boards.

In addition, it would be advantageous if the fiber-optic connectionscould be created prior to dicing the discrete PICs from the wafer; thisis often referred to as wafer-level attachment. Manufacturers ofintegrated circuits and PICs often have expensive capital equipmentcapable of sub-micron alignment (e.g. wafer probers and handlers fortesting integrated circuits), whereas companies that package chipsgenerally have less capable machinery (typically several micronalignment tolerances which is not adequate for single-mode devices) andoften use manual operations. However, it is impractical to permanentlyattach optical fibers to PICs prior to dicing since the optical fiberswould become tangled, would be in the way during the dicing operationsand packaging procedures, and are practically impossible to manage whenthe PICs are pick-and-placed onto printed circuit boards and thensoldered to the PCBs at high temperatures.

US Patent Publication No. 2016/0161686A1 (commonly assigned to theassignee of the present application, and fully incorporated by referenceherein) discloses demountable optical connectors for optoelectronicdevices. The disclosed demountable optical connectors includeimplementation of an elastic averaging coupling to provide an improvedapproach to optically couple input/output of optical fibers to PICswhich improves tolerance, manufacturability, ease of use, functionalityand reliability at reduced costs. As is known in the prior art, elasticaveraging represents a subset of surface coupling types where improvedaccuracy is derived from the averaging of error over a large number ofcontacting surfaces. Contrary to kinematic design, elastic averaging isbased on significantly over-constraining the solid bodies with a largenumber of relatively compliant members. As the system is preloaded, theelastic properties of the material allow for the size and position errorof each individual contact feature to be averaged out over the sum ofcontact features throughout the solid body. Although the repeatabilityand accuracy obtained through elastic averaging may not be as high as indeterministic systems, elastic averaging design allows for higherstiffness and lower local stress when compared to kinematic couplings.In a well-designed and preloaded elastic averaging coupling, therepeatability is approximately inversely proportional to the square rootof the number of contact points.

Most PIC devices require single-mode optical connections that requirestringent alignment tolerances between optical fibers and the PIC,typically less than 1 micrometer. Efficient optical coupling to and fromthe on-chip single-mode waveguides to an external optical fiber ischallenging due to the mismatch in size between the single-modewaveguides and the light-guiding cores within optical fibers. Forexample, the dimension of a typical silica optical fiber isapproximately forty times larger than a typical waveguide on a PIC.Because of this size mismatch, if the single mode waveguide and theoptical fiber are directly coupled, the respective modes of thewaveguide and optical fiber may not couple efficiently resulting in anunacceptable insertion loss (e.g., >20 dB).

US Patent Publication No. 2020/0124798A1 (commonly assigned to theassignee of the present application, and fully incorporated by referenceherein) discloses demountable edge couplers with micro-mirror opticalbench for PICs, which provide a mechanism to bring the mode sizes of theoptical fibers in a fiber array and on-chip optical elements close toeach other to effectuate efficient optical coupling input/output ofoptical fibers to PIC devices.

What is needed is an improved demountable optical coupling betweenconnectors, based on an improved elastic averaging approach that furtherimproves tolerance, manufacturability, ease of use, functionality andreliability at reduced costs.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of the prior art byproviding a demountable/separable and reconnectable passive alignmentcoupling/connection that achieve high alignment accuracy. An opticalconnector (e.g., supporting or is a part of an optical bench thatsupports an optical fiber) is configured and structured to benon-destructively, removably attachable for reconnection to thefoundation in alignment therewith. The foundation may be an integralpart of the opto-electronic device (e.g., part of a photonic integratedcircuit (PIC) chip), or a separate component attached to theopto-electronic device.

The present invention will be explained in connection with theillustrated embodiments. The foundation can be aligned toelectro-optical elements (e.g., grating couplers, waveguides, etc.) inthe optoelectronic device. The foundation is permanently positioned withrespect to the opto-electronic device to provide an alignment referenceto the external optical connector. The optical connector can beremovably attached to the foundation, via a ‘separable’ or ‘demountable’or ‘detachable’ action that accurately optically aligns the opticalcomponents/elements in the optical bench to the opto-electronic devicealong a desired optical path. In order to maintain optical alignment foreach connect and disconnect and reconnect, this connector needs to beprecisely and accurately aligned to the foundation. In accordance withthe present invention, the connector and foundation are aligned with oneanother using a passive mechanical alignment, specifically, elasticaveraging alignment, constructed from geometric features on the twobodies. With the foregoing as introduction, the present invention may besummarized below.

The present invention is directed to a passive optical alignmentcoupling for an optical connector and a foundation (e.g., associatedwith a PIC chip). The optical connector comprises a first bodytransmitting an optical signal. The first body defines a first base(which may support an optical fiber array) having a first, planar,surface defined with a first two-dimensional planar array of alignmentfeatures integrally defined on the first surface of the first base; andthe foundation (which may be coupled to a photonic integrated circuitPIC) comprising a second body providing an alignment reference to anexternal optoelectronic device communicating optical signals with theoptical connector. The second body defines a second base having asecond, planar, surface defined with a second two-dimensional planararray of alignment features integrally defined on the second surface ofthe second base. One of the first array of alignment features and thesecond array of alignment features comprises a first network oforthogonally intersecting longitudinal open grooves, and the other oneof the first array of alignment features and the second array ofalignment features comprises a second network of longitudinalcylindrical protrusions (each may be a continuous cylindrical protrusionor a broken chain of cylindrical protrusions) each having a longitudinalaxis parallel to corresponding one of the first surface of the firstbase or the second surface of the second base. (Alternatively, thealignment features on the optical connector and the foundation may beswapped.) The second network of cylindrical protrusions are received inthe matching complementary first network of open grooves, withprotrusion surfaces of the cylindrical protrusions in contact withgroove surfaces of the longitudinal grooves. The optical connector isremovably attachable to the foundation to define a demountable coupling,with the first array of alignment features against the second array ofalignment features to define an elastic averaging coupling, therebyaligning the optical connector to the foundation.

In one embodiment, the first network of orthogonally intersectinglongitudinal grooves of the first alignment features define an array ofdiscrete protrusions separated and isolated from one another by theorthogonally intersecting longitudinal grooves on the first surface ofthe first base (or alternatively on the second surface of the secondbase), which are each in a generally pyramidal shape with a truncatedtop (e.g., a flat or slightly convex curved top). The array of discreteprotrusions may comprise raised structures each symmetrical with respectto a first plane orthogonal to the corresponding one of the firstsurface of the first base and the second surface of the second base andfurther symmetrical with respect to a second plane orthogonal to thefirst plane and orthogonal to the corresponding one of the first surfaceand the second surface (i.e., the raised structures are each symmetricalalong two orthogonal planes about a central axis orthogonal to the firstsurface of the first base of the optical connector (or alternatively onthe second surface of the second base of the foundation).

In one embodiment, the second network of cylindrical protrusionscomprises a network of intersecting longitudinal cylindrical protrusions(forming a cross-grid structure on the surface of the correspondingbase), each may be, in one embodiment, substantially semi-circularprofile in cross-section. Other convex curved cross-section (e.g.,elliptic, parabolic, or gothic arch profiles) may be adopted.

In one embodiment, the protrusion surfaces of the longitudinalcylindrical protrusions are in line contact with the groove surfaces todefine an array of line contacts when the optical connector is coupledto the foundation. In this embodiment, the longitudinal grooves areV-grooves, and each discrete protrusion comprises substantially flatsurfaces corresponding to the groove surfaces so as define the linecontacts with the protrusion surfaces when the optical connector iscoupled to the foundation. In another embodiment, the protrusionsurfaces of the longitudinal cylindrical protrusions are in pointcontact with the groove surfaces to define an array of point contactswhen the optical connector is coupled to the foundation. In thisembodiment, each discrete protrusion comprises convex curved surfacescorresponding to the groove surfaces so as to define the point contactswith the protrusion surfaces when the optical connector is coupled tothe foundation.

In one embodiment, the array of discrete protrusions is a rectangulararray of (M+1)×(N+1) discrete protrusions corresponding to the firstnetwork of intersecting grooves comprising M×N orthogonally intersectinglongitudinal grooves. The second network of cylindrical protrusionscomprises M×N orthogonally intersecting longitudinal cylindricalprotrusions, to match the first network of M×N intersecting longitudinalgrooves. For a coupling interface between the first surface of theoptical connector and the second surface of the foundation having aplanar area of about 3 mm×3 mm, to achieve a coupling accuracy of lessthan 1 micrometer between the optical connector and the foundation, M ispreferably in a range of 3 to 10 and N is in a range of 3 to 10.

In one embodiment, the discrete protrusions defined by the longitudinalgrooves contact the corresponding one of the first surface and thesecond surface, when the optical connector is coupled to the foundation.Further, in one embodiment, to ensure the optical connector seats on thefoundation in a predetermined unique position, the array of discreteprotrusions further comprise a plurality of guide key protrusions havingraised structures located along a perimeter/an edge of the first surface(or alternatively the second surface), which have a different surfaceprofile at the surfaces facing away from the perimeter/edge (i.e., thesurfaces not contacting a cylindrical protrusion when the opticalconnector is coupled to the foundation) as compared to the surfaceprofile of the symmetrical discrete protrusions located interior of theperimeter/edge (i.e., the discrete protrusions that contacts thecorresponding one of the first surface and the second surface). Forexample, some of the discrete protrusions at the perimeter of a 10×5array of discreate protrusions (i.e., M=9 and N=4), e.g., at the corners(1, 1), (10, 1), (1, 5) and (10, 5), may each include a surface profilethat is different from that of the discrete protrusions at interiorlocations away from the perimeter in the array (e.g., at (2, 2) to (9,2), etc.). The shape of the corner protrusions would not fit in theinterior spaces bound by cylindrical protrusions on four sides on theopposing surface. The corner protrusions would fit only into the spacesat the corners on the opposing surface since they are not bound bycylindrical protrusions. Hence, guide keys are provided at the couplinginterface to initially guide the mating of the first array of alignmentfeatures and the second array of alignment features, so as to uniquelyseat the relative position of the complementary alignment features tocouple the optical connector to the foundation in a predeterminedintended relative position.

In one embodiment, the first base comprises a first malleable metalmaterial and the first array of alignment features of the opticalconnector are integrally defined on the first base by stamping themalleable metal material, and the second base comprises a secondmalleable material and the second array of alignment features areintegrally defined on the base by stamping the second malleable metalmaterial.

In one embodiment, the optical connector further comprises a firstmicro-mirror optical bench, which comprises the first base; a firstarray of mirrors defined on the first base, wherein each mirror includesa structured reflective surface profile that turns light between a firstlight path, along a first direction in a first plane substantiallyparallel to the first surface of the first base, and a second lightpath, along a second direction outside the first plane; and an array offiber grooves defined on the first base each receiving a section ofoptical fiber with its longitudinal axis along the first light path,with an end in optical alignment with a corresponding mirror along thefirst light path. In one embodiment, the foundation comprises a secondmicro-mirror optical bench, which comprises: the second base; and asecond array of mirrors defined on the second base, wherein each mirrorin the second array of mirrors includes a structured reflective surfaceprofile that turns light between a third light path, along a thirddirection in a second plane substantially parallel to the second surfaceof the second base, and a fourth light path, along a fourth directionoutside the second plane. In one embodiment, the first array of mirrorsand the first array of alignment features are simultaneously defined onthe first base by stamping a first body of metal blank and the secondarray of mirrors and the second array of alignment features aresimultaneously defined on the second base by stamping a second body ofmetal blank. By high-precision stamping to integrally/simultaneouslyform the passive alignment features and/or the micro optical bench (MOB)on the foundation and the optical connector, the components can beproduced economically in high or small volumes, while improvingtolerance, manufacturability, ease of use, functionality andreliability. The foundation and/or optical bench components should bemade of a stampable materials like ductile metals such as Kovar, Invar,stainless steel, aluminum. Preferably, the optical bench and foundationshould both have similar coefficients of thermal expansion (CTEs), sothat misalignment does not occur during temperature cycles andstress/strains are not generated.

In one embodiment, the first base of the optical connector has a firstreference surface at a first side of the first base and the second baseof the foundation has a second reference surface at a second side of thesecond base. The first reference surface and the second referencesurface are generally aligned by a compliant clip biasing the first baseagainst the second base with the first array of alignment featuresagainst the second array of alignment features.

In accordance with the present invention, the optical connector and thefoundation define a free space coupling without any refractive opticalelement disposed between the optical connector and the foundation toprovide reshaping of light. Further, the demountable elastic averagingcoupling between the optical connector and the foundation is definedwithout use of any complementary alignment pin and alignment hole.

The inventive elastic averaging coupling of the present invention may bedeployed in a photonic apparatus. In one embodiment, the photonicapparatus comprises a support; an optoelectronic device attached to atop surface of the support; and a passive optical alignment comprisingthe inventive elastic averaging coupling. The foundation is positionedrelative to the optoelectronic device, either on the optoelectronicdevice and/or the support, to define an aligned position for theoptoelectronic device to communicate optical signals with the opticalconnector removably/demountably coupled to the foundation. Theoptoelectronic device may comprise a photonic integrated circuit (PIC)chip comprising optical elements as an optical interface to external ofthe PIC chip. The foundation is in optical alignment with the opticalelements of PIC chip.

In one embodiment, the foundation comprises an edge coupler supported onthe support in optical alignment with respect to the PIC chip. Theoptical elements of the PIC chip route light to an edge of the PIC chip.The edge coupler may comprise an array of mirrors in optical alignmentwith the optical elements of the PIC chip, and light is transmittedalong a light path between a mirror in the array of mirrors and acorresponding optical element in the PIC chip.

The present invention is also directed to a method for providing ademountable connection between an optical connector and anoptoelectronic device, comprising providing a support; attaching theoptoelectronic device to a top surface of the support; and providing apassive optical alignment coupling as in any of the above claims,wherein the foundation is positioned relative to the optoelectronicdevice, either on the optoelectronic device and/or the support, andwherein the foundation defines an aligned position for theoptoelectronic device to communicate optical signals with the opticalconnector that is demountably coupled to the foundation.

In one embodiment, the optical connector is first coupled to thefoundation. The optical connector is actively aligned to theoptoelectronic device by positioning the foundation relative to theoptoelectronic device (e.g., a PIC chip or an optical I/O chip) toobtain an optimum optical signal between the optoelectronic device andthe optical connector (e.g., optical fibers supported by the opticalconnector). The location of the foundation is secured with respect tothe optoelectronic device at the aligned position (e.g., using a solderto tack the position of the foundation on a support for theoptoelectronic device, such as an interposer, a printed circuit board, asubmount, etc.). The optical connector is then demounted from thefoundation, and the foundation can be permanently attached to thesupport (e.g., reflowing the solder) without changing its position onthe support. Thereafter, the optical connector can be repeatedlyconnected and disconnected and reconnected to the foundationnon-destructively without losing the original optical alignment obtainedby active alignment between the optical connector and the optoelectronicdevice. Optical alignment in accordance with original active alignmentis maintained for each connect and disconnect and reconnect, toprecisely and accurately align the optical connector to the foundation.

In one embodiment, the foundation may be an integral part of theoptoelectronic device or the support for the optoelectronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of theinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings. In the following drawings, like referencenumerals designate like or similar parts throughout the drawings.

FIGS. 1A to 1C illustrate passive alignment features of an opticalconnector and a foundation, in accordance with one embodiment of thepresent invention.

FIGS. 2A to 2D illustrate elastic averaging coupling interface of theoptical connector to the foundation, in accordance with one embodimentof the present invention.

FIGS. 3A and 3B illustrate passive alignment features of an opticalconnector and a foundation, in accordance with another embodiment of thepresent invention.

FIGS. 4A to 4D illustrate elastic averaging coupling interface of theoptical connector to the foundation, in accordance with anotherembodiment of the present invention.

FIG. 5 illustrate guide key protrusions, in accordance with anotherembodiment of the present invention.

FIGS. 6A and 6B illustrate positioning of a foundation as an edgecoupler to a PIC chip, in accordance with one embodiment of the presentinvention.

FIGS. 7A to 7C illustrate connection of an optical connector to thefoundation, in accordance with one embodiment of the present invention.

FIGS. 8A to 8D illustrate a process of securing position of thefoundation for subsequent demountable connection, in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is described below in reference to various embodimentswith reference to the figures. While this invention is described interms of the best mode for achieving this invention's objectives, itwill be appreciated by those skilled in the art that variations may beaccomplished in view of these teachings without deviating from thespirit or scope of the invention.

The present invention overcomes the drawbacks of the prior art byproviding a demountable/separable and reconnectable passive alignmentcoupling/connection that achieve high alignment accuracy. An opticalconnector (e.g., supporting or is a part of an optical bench thatsupports an optical fiber) is configured and structured to benon-destructively, removably attachable for reconnection to thefoundation in alignment therewith. The foundation may be an integralpart of the opto-electronic device (e.g., part of a photonic integratedcircuit (PIC) chip), or a separate component attached to theopto-electronic device.

The elastic averaging coupling concept of the present invention isdiscussed hereinbelow by reference to the example of a PIC as anoptoelectronic device and an optical connector comprising an opticalbench, and optically coupling an input/output end of an opticalcomponent (e.g., an optical fiber) supported in the optical bench withthe optoelectronic device. The present invention may be applied toprovide removable/reconnectable form structures and parts used in otherfields.

FIGS. 1A to 1C illustrate passive alignment features of an opticalconnector 10 and a foundation 12, in accordance with one embodiment ofthe present invention. The optical connector 10 comprises a first bodyB1 supporting an optical fiber array (schematically shown by dotted lineFA) transmitting an optical signal. The foundation 12 comprises a secondbody B2 providing an alignment reference to an external optoelectronicdevice (e.g., a PIC chip 100 in FIG. 7 , or an I/O PIC chip 101 for theASIC chip (e.g. CPU, GPU, switch ASIC) 102 in FIG. 8 ) communicatingoptical signals with optical fiber OF in the optical connector 10.

The first body of the connector 10 defines a first base B1 supportingthe optical fiber array FA having a first, planar, surface S1 definedwith a first two-dimensional planar array of alignment features F1integrally defined on the first surface S1 of the first base B1. In thisembodiment, the connector 10 incorporates a micro optical bench OB forsupporting and aligning the optical fiber array FA. The optical fiberarray FA has a plurality of optical fibers OF protected by protectivebuffer and matrix/jacket layers P. The base B1 of the connector 10defines structured features including an alignment structure comprisingopen grooves G for retaining bare sections of optical fibers OF (havingcladding exposed, without protective buffer and matrix/jacket layers J),and structured reflective surfaces (e.g., eight mirrors M1) having aplane inclined at an angle relative to the greater plane of the base B1.The open grooves G are sized to receive and located to preciselyposition the end section of the optical fibers OF in alignment withrespect to a first array of mirrors M along a first optical path L1. Theend face (input/output end) of each of the optical fibers OF ismaintained at a pre-defined distance with respect to a correspondingmirror M1. In the embodiment of FIG. 6A, a transparent glass, quartz, orsapphire plate cover SP1 covers the exposed surfaces on the opticalbench OB to protect the mirrors M1. In one embodiment, the connector 10may be filled with index-matching epoxy between the mirror surfaces M1and the plate cover SP1.

In one embodiment, each mirror M1 is an exposed free surface of the baseB1 (i.e., surface exposed to air, or not internal within the body of thebase of the optical bench) having an exposed reflective free side facingaway from the base B1. The exposed reflective free side comprises astructured reflective surface profile at which light is directed to andfrom the optical fiber OF and to and from the foundation 12. Each mirrorM1 bends, reflects and/or reshapes an incident light. Depending on thegeometry and shape (e.g., curvature) of the structured reflectivesurface profile, the mirrors M may collimate, expand, or focus anincident light beam. For example, the structured reflective surfaceprofile may comprise one of the following geometrical shape/profiles:(a) ellipsoidal, (b) off-axis parabolic, or (c) other free-form opticalsurfaces. For example, the mirror surface, to provide optical power, mayhave a surface geometrical curvature function of any of the following,individually, or in superposition: ellipsoidal or hyperbolic conic foci,toroidal aspheric surfaces with various number of even or odd asphericterms, X-Y aspheric curves with various number of even or off terms,Zernike polynomials to various order, and various families of simplersurfaces encompassed by these functions. The surfaces may also befree-form surfaces with no symmetry along any plane or vector. Themirrors M may be defined on the base B by stamping a malleable metalmaterial. Various malleable metals, stampable with tool steels ortungsten carbide tools, may compose the body of the mirrors, includingany 300 or 400 series stainless steel, any composition of Kovar, anyprecipitation or solution hardened metal, and any alloy of Ag, Al, Au,Cu. At the long wavelengths above 1310 nm, aluminum is highly reflective(>98%) and economically shaped by stamping. The reflective surface ofthe portion of the metal comprising the mirror may be any of the metalsmentioned above, or any coating of highly reflective metal, applied bysputtering, evaporation, or plating process.

U.S. Pat. No. 7,343,770, commonly assigned to the assignee of thepresent invention, discloses a novel precision stamping system formanufacturing small tolerance parts. Such inventive stamping system canbe implemented to produce the structures of the connector 10 and thefoundation 12 disclosed herein (including the structures for the opticalbench OB discussed above, as well as the structures discussed below).These stamping processes involve stamping a malleable bulk metalmaterial (e.g., a metal blank or stock), to form the final surfacefeatures at tight (i.e., small) tolerances, including the reflectivesurfaces having a desired geometry in precise alignment with the otherdefined surface features. U.S. Patent Application Publication No.US2016/0016218A1, commonly assigned to the assignee of the presentinvention, further discloses a composite structure including a basehaving a main portion and an auxiliary portion of dissimilar metallicmaterials. The base and the auxiliary portion are shaped by stamping. Asthe auxiliary portion is stamped, it interlocks with the base, and atthe same time forming the desired structured features on the auxiliaryportion, such as a structured reflective surface, optical fiberalignment feature, etc. With this approach, relatively less criticalstructured features can be shaped on the bulk of the base with lesseffort to maintain a relatively larger tolerance, while the relativelymore critical structured features on the auxiliary portion are moreprecisely shaped with further considerations to define dimensions,geometries and/or finishes at relatively smaller tolerances. Theauxiliary portion may include a further composite structure of twodissimilar metallic materials associated with different properties forstamping different structured features. This stamping approach improveson the earlier stamping process in U.S. Pat. No. 7,343,770, in which thebulk material that is subjected to stamping is a homogenous material(e.g., a strip of metal, such as Kovar, aluminum, etc.). The stampingprocess produces structural features out of the single homogeneousmaterial. Thus, different features would share the properties of thematerial, which may not be optimized for one or more features. Forexample, a material that has a property suitable for stamping analignment feature may not possess a property that is suitable forstamping a reflective surface feature having the best light reflectiveefficiency to reduce optical signal losses.

The overall functional structures of the optical bench OB generallyresemble the structures of some of the optical bench embodimentsdisclosed in the assignee's earlier patent documents noted above (i.e.,fiber alignment grooves aligned with structured reflective surfaces, andaddition features to facilitate proper optical alignment). The earlierdisclosed composite structure and stamping technology may be adopted toproduce the connector 10 including the mirrors M1 in the optical benchOB, the grooves G and the first array of alignment features F1, andfurther the foundation 12 including the mirrors M2 and the second arrayof alignment features F2 discussed below. The respective alignmentfeatures F1 and F2 are formed on the respective planar surfaces S1 andS2, which facilitates alignment and/or accurate positioning theconnector 10 with respect to the foundation 12, and hence with respectto the PIC chip 100/chip 102 or I/O chip 101, as will be explained laterbelow.

The mirror M1 surface and optical fiber alignment structure in theoptical connector can be integrally/simultaneous formed by precisionstamping of a stock material (e.g., a metal blank or strip), whichallows the connector components to be produced economically in high orsmall volumes, while improving tolerance, manufacturability, ease ofuse, functionality and reliability. By forming the structure reflectivesurface, the passive alignment features (discussed below) and theoptical fiber alignment structure simultaneously in a same, single finalstamping operation, dimensional relationship of all features requiringalignment on the same work piece/part can be maintained in the finalstamping step. Instead of a punching operation with a single strike ofthe punch to form all the features on the optical bench, it isconceivable that multiple strikes may be implemented to progressivepre-form certain features on the optical bench, with a final strike tosimultaneously define the final dimensions, geometries and/or finishesof the various structured features on the optical bench, including themirror, optical fiber alignment structure/groove, passive alignmentfeatures discussed below, etc. that are required to ensure (or playsignificant role in ensuring) proper alignment of the respectivecomponents/structures along the design optical path.

Essentially, for the optical connector 10, the base B1 defines anoptical bench OB for aligning the optical fibers OF with respect to themirrors M1. By including the fiber grooves G on the same, singlestructure that also defines the mirrors M, the alignment of the endsections of the optical fibers OF to the mirrors M1 can be moreprecisely achieved with relatively smaller tolerances by a single finalstamping to simultaneous define the final structure on a single part, ascompared to trying to achieve similar alignment based on featuresdefined on separate parts or structures, or based on separate formingsteps. By forming the mirrors M1, the optical fiber alignment grooves Gsimultaneously in a same, single final stamping operation, dimensionalrelationship of all features/components requiring (or play a role inproviding) alignment on the same work piece/part can be maintained inthe final stamping step. Further, by the same token, the first array ofalignment features F1 can also be formed with the mirrors M1 and thegrooves G simultaneously in a same, single final stamping operation tomaintain dimensional relationship of all the features (i.e., grooves G,mirrors M1 and alignment features F1) to achieve a desired alignmentwith a small tolerance.

In the illustrated embodiment in FIGS. 1A to 1C, the first array ofalignment features F1 of the connector 10 comprises a first network oforthogonally intersecting longitudinal open groove LG1 and longitudinalopen groove LG2, which are each a V-groove with flat walls. In oneembodiment, the first network of orthogonally intersecting longitudinalgrooves LG1 and LG2 of the first alignment features F1 define an arrayof discrete protrusions P separated and isolated from one another by theorthogonally intersecting longitudinal grooves LG1 and LG2 on the firstsurface S1 of the first base B1, which are each in a generally pyramidalshape with four flat sloping surfaces GS and a truncated top T (e.g., aflat or slightly convex curved top). The tops T of the protrusion Pconforms generally to the first surface S1. Each discrete protrusions P(with the exception of the ones at the corners and/or at the edges, asfurther explained below) is a raised structure symmetrical with respectto a first plane orthogonal to the first surface S1 of the first base B1and further symmetrical with respect to a second plane orthogonal to thefirst plane and orthogonal to the first surface S1 (i.e., the raisedstructures are each symmetrical along two orthogonal planes about acentral axis A orthogonal to the first surface S1 of the first base B1).The features of the protrusions P are better depicted in the enlargedview in FIG. 1C. US Patent Publication No. 2020/0124798A1 (commonlyassigned to the assignee of the present application, and fullyincorporated by reference herein) discloses demountable edge couplerswith micro-mirror optical bench for PICs, which provide a mechanism tobring the mode sizes of the optical fibers in a fiber array and on-chipoptical elements close to each other to effectuate efficient opticalcoupling input/output of optical fibers to PIC devices. The foundation12 herein has a structure similar to the edge coupler, and in fact couldbe structured similar to the edge coupler disclosed earlier therein,except for the passive alignment features on the foundation 12 ascompared to the passive alignment features disclosed therein.

Referring to FIGS. 1A and 1B, the foundation 12 comprises a body havinga base B2 (e.g., made of silicon, glass, a malleable metal such asKovar, Invar, aluminum, stainless steel) with a second array of mirrorsM2 defined on the base B2. In the embodiment of FIG. 6B, a transparentglass, quartz, or sapphire plate cover SP2 covers the exposed surfaceson the base B2. In one embodiment, the foundation 12 may be filled withindex-matching epoxy between the mirror surfaces M2 and the plate coverSP2. The structure of the mirrors M2 on the base B2 of the foundation 12is quite similar to the corresponding structure of the mirrors M1 on thebase B1 of the connector 10. The optical geometries of the respectivemirrors M1 and M2 are chosen to implement the desired optical path. Inthe illustrated embodiment, the foundation 12 does not include anyoptical fiber as compared to the connector 10. However, the base B2 mayfurther define grooves receiving short sections of optical fibers (notshown) as waveguides communicating light signals to and from the mirrorsB2, as was in the case of the edge couplers disclosed in US PatentPublication No. 2020/0124798A1.

The base B2 of the foundation 12 has a second, planar, surface S2defined with a second two-dimensional planar array of alignment featuresF2 integrally defined on the second surface S2 of the second base B2.The second array of alignment features F2 of the foundation 12 comprisesa second network of longitudinal cylindrical protrusions (each may be acontinuous cylindrical protrusion or a broken chain or a row of separatecylindrical protrusions in a common axial direction of the separatecylindrical protrusions) each having a longitudinal axis parallel tocorresponding one of the second surface S2 of the second base B2. Inthis illustrated embodiment, the second network of cylindricalprotrusions comprises a network of intersecting longitudinal cylindricalprotrusions LP1 and longitudinal cylindrical protrusions LP2 (formingcross-grid protruded structure as shown in FIGS. 1A and 1B), each havinga substantially semi-circular profile in cross-section. Other convexcurved cross-section (e.g., elliptic, parabolic, or gothic archprofiles) may be adopted.

FIGS. 2A to 2D illustrate elastic averaging coupling interface of theoptical connector to the foundation, in accordance with one embodimentof the present invention. FIG. 2A is a view of the coupling of theconnector 10 on the foundation 12 viewed at an end in a direction alongthe longitudinal axis of the optical fiber OF. FIG. 2A is an enlargedview of the contact surfaces between the first and second arrays ofalignment features. FIGS. 2C and 2D (an enlarged sectional view) showthe sectional view taken along line 2C-2C in FIGS. 2A and 2C. The secondnetwork of orthogonal cylindrical protrusions LP1 and LP2 are receivedin the complementary matching first network of orthogonal open groovesLG1 and LG2. The protrusion surfaces of the cylindrical protrusions LP1and LP2 contact the groove surfaces GS of the longitudinal grooves LG1and LG2.

As can be seen in FIG. 2B, the longitudinal grooves LG1 are each aV-groove having flat groove wall surfaces in its longitudinal direction,and each discrete protrusion P comprises substantially flat slopingsurfaces corresponding to the V-groove surfaces. The flat surfaces ofthe V-grooves LG1 and the convex curved surfaces of the cylindricalprotrusions LP1 define line contacts LC between adjacent cylindricalprotrusions LP2 (as depicted in FIGS. 2C and 2D) when the opticalconnector 10 is coupled to the foundation 12. Hence, the protrusionsurfaces of the network of intersecting longitudinal cylindricalprotrusions LP1 and LP2, being a straight surface in their respectivelongitudinal direction, are in line contact with the flat surfaces ofthe network of intersecting longitudinal grooves LG1 and LG2 to definean array of line contacts LC when the optical connector 10 is coupled tothe foundation 12. The plurality of line contacts corresponds to anelastic averaging coupling so that the optical connector 10 can beremovably attachable to the foundation to define a demountable coupling,with the first array of alignment features F1 against the second arrayof alignment features F2 to define an elastic averaging coupling,thereby aligning the optical connector to the foundation. It is notedthat to achieve line contacts LC, the cylindrical protrusions LP1 andLP2 each may be a broken chain of discrete/isolated cylindricalprotrusions along an axial direction parallel to the base B2 of thefoundation 12, as long as a cylindrical protrusion surface is present inthe region of interface with the flat surfaces GS of each discreteprotrusions P. In other words, the cylindrical protrusions LP1 and LP2do not need to be physically intersecting to form the cross-gridstructure as shown in FIGS. 1A and 1B.

FIGS. 3A and 3B illustrate passive alignment features of an opticalconnector and a foundation, in accordance with another embodiment of thepresent invention. In this embodiment, the foundation 12 remains similarto the embodiment depicted in FIG. 1 . The connector 10 is generallysimilar to the previous embodiment, with modifications to the structuresof the intersection longitudinal grooves LG1′ and LG2′ and the discreteprotrusions P′. The protrusions P′ are each of a generally pyramidalshape, having convex curved surfaces GS′ corresponding to the groovesurfaces GS′ and a flat or convex top T. The intersecting longitudinalgrooves LG1′ and LG2′ are no longer V-grooves with flat wall surfaces asis the case in the previous embodiment of FIG. 1 . In this embodiment,the longitudinal grooves LG1′ and LG2′ are generally V-shaped grooveseach having side walls with convex surfaces corresponding to theprotrusions P′. In particular, the protrusions P′ has sloping surfacesGS′ that is convex at least in the direction along the longitudinalgrooves. It is noted that the sloping surfaces GS′ may also curve in theheight direction or in a direction of the slope, or a combinationthereof.

FIGS. 4A to 4D illustrate elastic averaging coupling interface of theoptical connector 10 to the foundation 12, in accordance with theembodiment of FIGS. 3A and 3B. The views in FIG. 4 corresponds to theviews in FIG. 2 discussed above, which provide comparison to theprevious embodiment.

As can be in FIG. 4B, the longitudinal grooves LG1′ are each a generallyV-shaped grooves, and each discrete protrusion P′ comprises convexsloping surfaces GS′ corresponding to the groove surfaces GS′. Theconvex surfaces GS′ of the grooves LG1′ and the convex curved surfacesof the cylindrical protrusions LP1 define point contacts PC betweenadjacent cylindrical protrusions LP2 (as depicted in FIGS. 4C and 4D)when the optical connector 10 is coupled to the foundation 12. Hence,the protrusion surfaces of the network of intersecting longitudinalcylindrical protrusions LP1 and LP2, being a straight surface in theirrespective longitudinal direction, are therefore in point contact withthe convex surfaces GS′ of the network of intersecting longitudinalgrooves LG1′ and LG2′, to define an array of line contacts PC when theoptical connector 10 is coupled to the foundation 12. The plurality ofpoint contacts PC correspond to an improved elastic averaging couplingso that the optical connector 10 can be removably attachable to thefoundation to define a demountable coupling, with the first array ofalignment features F1 against the second array of alignment features F2to define an elastic averaging coupling, thereby aligning the opticalconnector to the foundation. It is noted that given the point contactsPC, the cylindrical protrusions LP1 and LP2 each may be a broken chainof discrete/isolated cylindrical protrusions along an axial directionparallel to the base B2 of the foundation, as long as a cylindricalprotrusion surface is present in the region of interface with the convexsurfaces GS′ of each discrete protrusions P′. In other words, thecylindrical protrusions LP1 and LP2 do not need to be physicallyintersecting to form the cross-grid structure as shown in FIG. 1 .

The array of discrete protrusions (P, P′) is a rectangular array of(M+1)×(N+1) discrete protrusions corresponding to the first network ofintersecting grooves comprising M×N orthogonally intersectinglongitudinal grooves (LG1, LG2; LG1′ and LG2′). The second network ofcylindrical protrusions comprises M×N orthogonally intersectinglongitudinal cylindrical protrusions LP1 and LP2, to match the firstnetwork of M×N intersecting longitudinal grooves. In both embodimentsdepicted in FIGS. 2 and 4 , M=10 and N=4 only for purposes ofillustration. For a coupling interface between the first surface S1 ofthe optical connector 10 and the second surface S2 of the foundation 12having a planar area of about 3 mm×4 mm, to achieve a coupling accuracyof less than 1 micrometer between the optical connector and thefoundation, M is preferably in a range of 3 to 10 and N is in a range of3 to 10.

Referring the embodiment of FIG. 2B, the discrete protrusions P definedby the network of intersecting longitudinal grooves LG1 and LG2 on theconnector 10 contact the second surface S2 in the space between adjacentcylindrical protrusions LP1 of the foundation 12, when the opticalconnector 10 is coupled to the foundation 12. Similarly, in theembodiment of FIG. 4B, the discrete protrusions P′ defined by theintersecting longitudinal grooves LG1′ and LG2′ on the connector 10contact the second surface S2 in the space between adjacent cylindricalprotrusions LP1 of the foundation 12, when the optical connector 10 iscoupled to the foundation 12.

In one embodiment, referring to FIG. 1C, to ensure the optical connector10 seats on the foundation 12 in a predetermined unique position, thearray of discrete protrusions P further comprise a plurality of guidekey protrusions GP having raised structures located along theperimeter/edge of the first surface S1, which have a different surfaceprofile at the surfaces facing away from the perimeter/edge (i.e., thesurfaces not contacting a cylindrical protrusion when the opticalconnector is coupled to the foundation) as compared to the surfaceprofile of the symmetrical discrete protrusions P located interior ofthe perimeter/edge (i.e., the discrete protrusions P that contact thesecond surface S2 of the foundation 12. As depicted in FIG. 1C, theprotrusions GP along the perimeter of the first surface S1 each has astraight wall surface W facing away from the perimeter. Given the wallsurfaces W, the shape of the protrusions GP would not fit in theinterior spaces bound by cylindrical protrusions LP1 and LP2 on foursides on the opposing surface S2. However, the protrusions GP would fitonly into the spaces along the edges on the opposing surface S2 sincethe straight wall surfaces W are not bound by cylindrical protrusions atthe edges.

FIG. 5 illustrate an embodiment of guide key protrusions that may beimplemented for convex protrusion surfaces GS′ in the embodiment of FIG.3 . For example, for the illustrated 10×5 array of discreate protrusionsP′ (i.e., M=9 and N=4), the discrete protrusions GP′ at the corners (1,1), (10, 1), (1, 5) and (10, 5), may each include a surface profile atthe surfaces facing away from the perimeter/edge as shown which isdifferent from that of the discrete protrusions P′ at interior locationsaway from the perimeter in the array (e.g., at (2, 2) to (9, 2), etc.).Given the shape of the corner protrusions GP′, they would not fit in theinterior spaces bound by cylindrical protrusions LP1 and LP2 on foursides on the opposing surface S2. The corner protrusions GP′ would fitonly into the spaces at the corners on the opposing surface S2 sincethey are not completely bound by cylindrical protrusions LP1 and LP2 atthe corner.

Hence, guide keys such as GP and GP′ can be provided at the couplinginterface to guide the first array of alignment features F1 and thesecond array of alignment features F2 to uniquely seat the relativeposition of the complementary alignment features to couple the opticalconnector 10 to the foundation 12 in a predetermined intended relativeposition.

It is understood that alternatively, the longitudinal groove andlongitudinal cylindrical protrusion alignment features disclosed in theabove described embodiments may be swapped between the interfacingsurfaces of the optical connector 10 and the foundation 12, withoutdeparting from the scope and spirit of the present invention.

In one embodiment, the first base B1 comprises a first malleable metalmaterial and the first array of alignment features F1 of the opticalconnector 10 are integrally defined on the first base by stamping themalleable metal material, and the second base B2 comprises a secondmalleable material and the second array of alignment features F2 of thefoundation are integrally defined on the base by stamping the secondmalleable metal material. In one embodiment, the first array of mirrorsM1 and the first array of alignment features F1 are simultaneouslydefined on the first base by stamping a first body of metal blank andthe second array of mirrors M2 and the second array of alignmentfeatures F2 are simultaneously defined on the second base by stamping asecond body of metal blank. By high-precision stamping tointegrally/simultaneously form the passive alignment features and/or themicro optical bench (MOB) on the foundation and the optical connector,the components can be produced economically in high or small volumes,while improving tolerance, manufacturability, ease of use, functionalityand reliability. The foundation and/or optical bench components shouldbe made of a stampable materials like ductile metals such as Kovar,Invar, stainless steel, aluminum. Preferably, the optical bench andfoundation should both have similar coefficients of thermal expansion(CTEs), so that misalignment does not occur during temperature cyclesand stress/strains are not generated.

FIGS. 6A and 6B illustrate positioning of a foundation 12 as an edgecoupler to a PIC chip 100, in accordance with one embodiment of thepresent invention. As shown, the foundation 12 is butted against the PICchip 100 or positioned with a gap between the edge of the base B2 of thefoundation and the facing edge of the PIC chip 100 (as shown in FIG.7C), with the cover SP2 extending over the PIC chip 100. In thisembodiment, the foundation 12 is supported on the support S in opticalalignment with respect to the PIC chip 100. The optical elements of thePIC chip 100 route light to an edge of the PIC chip 100. The foundation12 functions as an edge coupler. As explained above, the array ofmirrors M2 of the foundation 12 are in optical alignment with theoptical elements of the PIC chip 100, and light is transmitted along alight path L3 between a mirror M2 in the mirror array and acorresponding optical element in the PIC chip 100.

In the embodiment shown in FIG. 6A, optical alignment of the mirrors M2in the foundation 12 and the optical elements in the PIC chip 100 isachieved by passive alignment of the mirror M2 to the edge of the PICchip based on fiducials V provided on an extended section of cover SP2beyond the edge of the base B2 of the foundation 12 and fiducials (notshown) provided at a top surface near the edge of the PIC chip 100. Thegap can be filled with a material that has an optical index ofrefraction that is similar to that of the core of the optical fiber andwaveguide on the PIC chip 100. The foundation 12 is passively aligned tothe PIC chip 100 by optically aligning the fiducials V on the cover SP2to the fiducials (not shown) provided on the top surface of the PIC chip100. In another embodiment, the foundation 12 may be an integral part ofthe PIC chip 100 or the support S for the PIC chip 100.

FIGS. 7A to 7C illustrate the connection of the optical connector 10 tothe foundation 12, in accordance with one embodiment of the presentinvention. The PIC chip 100 is supported on a support S (which may be asubmount, interposer), which may be supported on a printer circuit boardPCB in FIG. 7B. The first base B1 of the optical connector 10 has afirst reference surface R1 at least at one side of the first base B1 andthe second base B2 of the foundation 12 has at least a second referencesurface R2 at a second side of the second base B2. The first referencesurface R1 and the second reference surface R2 are generally aligned bya compliant clip C biasing the first base B1 against the second base B2with the first array of alignment features F1 seated against the secondarray of alignment features F2. In FIG. 7B, the optical fiber array FAmay be a fiber-optic jumper cable to provide a flexible opticalconnection for optical signal communication with the PIC chip 100.

FIG. 7C is a sectional view taken along line 7A-7A in FIG. 7A. Themirrors M1 each includes a structured reflective surface profile thatturns light (e.g., by 90 degrees) between a first light path L1, along afirst direction in a first plane substantially parallel to the firstsurface S1 of the first base B1 of the connector 10, and a second lightpath L2, along a second direction outside the first plane. The array offiber grooves G defined on the first base B1 each supports an endsection of optical fiber OF in optical alignment with a correspondingmirror M1 along the first light path L1. The second array of mirrors M2defined on the second base B2 of the foundation each includes astructured reflective surface profile that turns light between a thirdlight path L3 along a third direction in a second plane substantiallyparallel to the second surface S2 of the second base B2, and a fourthlight path L4 along a fourth direction outside the second plane. Thelight paths L3 and L4 coincide upon coupling the connector 10 andfoundation 12 in the configuration shown, so that a light path iscompleted between the PIC chip 100 and the optical fibers OF in thefiber array FA.

The structured reflective surface profile of the mirrors M1 and/ormirrors M2 may be configured to reshape the light beam from the PIC chip100 to produce a mode field that more closely match the mode field ofthe optical fibers OF in the connector 10. Further, the mirrors M2 inthe foundation 12 may be configured with a reflective surface profile toexpand or collimate the light beams from the optical elements in the PICchip 100 and output to the mirrors M1 in the connector 10, and themirrors M1 in the connector 10 may be configured with a reflectivesurface profile to focus the light beams from the mirrors M2 in thefoundation 12 to focus on the core of the tip/end face of the opticalfiber OF held in the grooves G on the base B1 of the optical bench inthe connector 10. This expanded beam optical coupling configurationwould reduce optical alignment tolerance requirement between the mirrorsM2 and the optical fibers OF held in the connector 10.

FIGS. 8A to 8D illustrate a process of securing position of thefoundation 12 for subsequent demountable connection, in accordance withone embodiment of the present invention. In this embodiment, additionalI/O chips 101 are provided to interface with the ASIC (e.g. CPU, GPU,switch ASIC) chip 102. The optical path is similar to the optical pathshown in FIG. 7C, with the I/O chip 101 replacing the PIC chip 100. Theoptical connector 10 is first coupled to the foundation 12 in FIG. 8A.The optical connector 10 is actively aligned to a chip 101 bypositioning the foundation 12 relative to the chip 101 to obtain anoptimum optical signal between the chip 101/chip 102 and the opticalfibers OF supported by the optical connector 10. The location of thefoundation 12 is secured with respect to the chip 101 at the opticallyaligned position (e.g., using a solder to tack the position of thefoundation 12 on the support S for the chip 101 (such as an interposer,a printed circuit board, a submount, etc.). In FIG. 8B, the opticalconnector 10 is then demounted from the foundation 12. In FIG. 8C, thefoundation 12 can be permanently attached to the support S (e.g.,reflowing the solder) without changing its position on the support S.Thereafter, in FIG. 8D, the optical connector 10 can be repeatedlyconnected and disconnected and reconnected to the foundation 12,non-destructively and without losing the original optical alignmentobtained by active alignment between the optical connector 10 and thechip 101/chip 102. Optical alignment in accordance with original activealignment is maintained for each connect and disconnect and reconnect,to precisely and accurately align the optical connector 10 to thefoundation 12.

In accordance with the present invention, the optical connector and thefoundation define a free space coupling without any refractive opticalelement disposed between the optical connector and the foundation toprovide reshaping of light. Further, the demountable elastic averagingcoupling between the optical connector and the foundation is definedwithout use of any complementary alignment pin and alignment hole.

While the invention has been particularly shown and described withreference to the preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and detail may be madewithout departing from the spirit, scope, and teaching of the invention.Accordingly, the disclosed invention is to be considered merely asillustrative and limited in scope only as specified in the appendedclaims.

We claim:
 1. A passive optical alignment coupling, comprising: anoptical connector comprising a first body transmitting an opticalsignal, wherein the first body defines a first base having a first,planar, surface defined with a first two-dimensional planar array ofalignment features integrally defined on the first surface of the firstbase, a foundation comprising a second body providing an alignmentreference to the optical connector, wherein the second body defines asecond base having a second, planar, surface defined with a secondtwo-dimensional planar array of alignment features integrally defined onthe second surface of the second base, wherein one of the first array ofalignment features and the second array of alignment features comprisesa first network of orthogonally intersecting longitudinal grooves, andanother one of the first array of alignment features and the secondarray of alignment features comprises a second network of longitudinalcylindrical protrusions each having a longitudinal axis parallel tocorresponding one of the first surface of the first base or the secondsurface of the second base, wherein the second network of cylindricalprotrusions are received in the first network of grooves, withprotrusion surfaces of the cylindrical protrusions in contact withgroove surfaces of the grooves, and wherein the optical connector isremovably attachable to the foundation to define a demountable coupling,with the first array of alignment features against the second array ofalignment features to define an elastic averaging coupling, therebyaligning the optical connector to the foundation.
 2. A passive alignmentcoupling, comprising: a first body defining a first base having a first,planar, surface defined with a first two-dimensional planar array ofalignment features integrally defined on the first surface of the firstbase, a second body providing an alignment reference to the first body,wherein the second body defines a second base having a second, planar,surface defined with a second two-dimensional planar array of alignmentfeatures integrally defined on the second surface of the second base,wherein one of the first array of alignment features and the secondarray of alignment features comprises a first network of orthogonallyintersecting longitudinal grooves, and another one of the first array ofalignment features and the second array of alignment features comprisesa second network of longitudinal cylindrical protrusions each having alongitudinal axis parallel to corresponding one of the first surface ofthe first base or the second surface of the second base, wherein thesecond network of cylindrical protrusions are received in the firstnetwork of grooves, with protrusion surfaces of the cylindricalprotrusions in contact with groove surfaces of the grooves, and whereinthe first body is removably attachable to the second body to define ademountable coupling, with the first array of alignment features againstthe second array of alignment features to define an elastic averagingcoupling, thereby aligning the first body to the second body.
 3. Thepassive alignment coupling as in claim 2, wherein the first network oforthogonally intersecting longitudinal grooves of the first alignmentfeatures define an array of discrete protrusions separated and isolatedfrom one another by the orthogonally intersecting longitudinal grooveson the corresponding one of the first surface of the first base and thesecond surface of the second base, which are each in a generallypyramidal shape with a truncated top.
 4. The passive alignment couplingas in claim 3, wherein the array of discrete protrusions comprise raisedstructures each symmetrical with respect to a first plane orthogonal tothe corresponding one of the first surface of the first base and thesecond surface of the second base and further symmetrical with respectto a second plane orthogonal to the first plane and orthogonal to thecorresponding one of the first surface and the second surface.
 5. Thepassive alignment coupling as in claim 4, wherein the array of discreteprotrusions further comprise a plurality of key guide protrusions havingraised structures located along a perimeter/an edge of the correspondingone of the first surface and the second surface, which have a differentsurface profile at the surfaces facing away from the perimeter/edge ascompared to that of the symmetrical discrete protrusions locatedinterior of the perimeter/edge, thereby to initially guide the relativeposition of the first and second arrays of alignment features touniquely seat the relative position of the first body having the firstarray of alignment features and the second body having the second arrayof alignment features to couple the first body to the second body in apredetermined, intended relative position.
 6. The passive alignmentcoupling as in claim 3, wherein the array of discrete protrusions is arectangular array of (M+1)×(N+1) discrete protrusions, wherein the firstnetwork of intersecting grooves comprises M×N orthogonally intersectinglongitudinal grooves, and wherein M is preferably in a range of 3 to 10and N is in a range of 3 to 10 for a coupling interface between thefirst body and the second body having a planar area of about 3 mm×3 mm,so as to achieve a coupling accuracy of less than 1 micrometer betweenthe first body and the second body.
 7. The passive alignment coupling asin claim 3, wherein the discrete protrusions defined by the longitudinalgrooves contact the corresponding one of the first surface and thesecond surface, when the first body is coupled to the second body. 8.The passive alignment coupling as in claim 2, wherein the protrusionsurfaces of the longitudinal cylindrical protrusions are in line contactwith the groove surfaces to define an array of line contacts when thefirst body is coupled to the second body, and wherein the longitudinalgrooves are V-grooves, and wherein each discrete protrusion comprisessubstantially flat surfaces corresponding to the groove surfaces so asdefine the line contacts with the protrusion surfaces when the firstbody is coupled to the second body.
 9. The passive alignment coupling asin claim 2, wherein the protrusion surfaces of the longitudinalcylindrical protrusions are in point contact with the groove surfaces todefine an array of point contacts when the first body is coupled to thesecond body, and wherein each discrete protrusion comprises convexcurved surfaces corresponding to the groove surfaces so as to define thepoint contacts with the protrusion surfaces when the first body iscoupled to the second body.
 10. The passive alignment coupling as inclaim 2, wherein the second network of cylindrical protrusions comprisesa network of intersecting longitudinal cylindrical protrusions.
 11. Thepassive alignment coupling as in claim 10, wherein the second network ofcylindrical protrusions comprises M×N orthogonally intersectinglongitudinal cylindrical protrusions, matching the first network ofintersecting longitudinal grooves.
 12. The passive alignment coupling asin claim 2, wherein the second network of cylindrical protrusions areeach substantially semi-circular in cross-section.
 13. The passivealignment coupling as in claim 2, wherein the first base comprises afirst malleable metal material and the first array of alignment featuresof the first body is integrally defined on the first base by stampingthe malleable metal material, and the second base comprises a secondmalleable material and the second array of alignment features isintegrally defined on the base by stamping the second malleable metalmaterial.
 14. The passive alignment coupling as in claim 2, wherein thefirst body comprises a first micro-mirror optical bench, whichcomprises: the first base; a first array of mirrors defined on the firstbase, wherein each mirror includes a structured reflective surfaceprofile that turns light between a first light path, along a firstdirection in a first plane substantially parallel to the first surfaceof the first base, and a second light path, along a second directionoutside the first plane; and an array of fiber grooves defined on thefirst base each receiving a section of optical fiber with itslongitudinal axis along the first light path, with an end in opticalalignment with a corresponding mirror along the first light path. 15.The passive alignment coupling as in claim 14, wherein the second bodycomprises a second micro-mirror optical bench, which comprises: thesecond base; and a second array of mirrors defined on the second base,wherein each mirror in the second array of mirrors includes a structuredreflective surface profile that turns light between a third light path,along a third direction in a second plane substantially parallel to thesecond surface of the second base, and a fourth light path, along afourth direction outside the second plane.
 16. The passive alignmentcoupling as in claim 15, further comprising a compliant clip biasing thefirst body against the second body with the first array of alignmentfeatures against the second array of alignment features.
 17. The passivealignment coupling as in claim 15, wherein the first array of mirrors issimultaneously defined with the first array of alignment features on thefirst base and the second array of mirrors is simultaneously definedwith the second array of alignment features on the second base.
 18. Thepassive alignment coupling as in claim 14, wherein the first body iscomprised in an optical connector transmitting an optical signal. 19.The passive alignment coupling as in claim 18, wherein the second bodyis comprised in a foundation providing an optical alignment reference.20. The passive alignment coupling as in claim 19, wherein thefoundation provides an optical alignment reference to an externaloptoelectronic device.
 21. The passive alignment coupling as in claim 2,wherein the first body and the second body define a free space couplingwithout any refractive optical element disposed between the first bodyand the second body.
 22. The passive alignment coupling as in claim 2,wherein the demountable coupling between the first body and the secondbody is defined without use of any complementary alignment pin andalignment hole.
 23. The passive alignment coupling as in claim 2,wherein at least one of the first body and the second body comprises atleast one optical waveguide.